Method of manufacturing semiconductor devices having element separating regions

Abstract: Buried type element separating trenches suitable for microminiaturization of semiconductor circuits can be formed. In addition, such defects as to generate electric field concentration and gate oxide film leakage due the shape of the element separating trenches can be prevented effectively. The method of manufacturing a semiconductor device, comprises the steps of: forming a first material layer (3) and a second material layer (5) in sequence on a surface of a semiconductor substrate (1); forming a first opening on the first material layer (3) and a second opening in the second material layer (5) (the first opening being larger than the second opening); forming an element separating trench (7) under the second opening in the substrate (1) by using the second material layer (5) as a mask; removing the second material layer (5); depositing a filling material (9) on the element separating trench (7), the substrate (1) and the first material layer (3); and etching back the filling material (9) by using the first material layer (3) as a stopper. In the above-mentioned process, the filling material remains over and about the element separating trench so as to cover the edge portion between the substrate surface and the separating trench, thus eliminating the edge portion which causes defects.

Description: The present invention relates to a method of manufacturing semiconductor devices, and more specifically to a method of manufacturing semiconductor devices having buried element separating regions. Reference is made to EP-A-0048175, which discloses a semiconductor device having a plurality of elements isolated by a groove which is at least partly filled with insulating material. To avoid risk of breakage of conductive layers later formed on the groove, the groove has a gentle slope at its upper side wall portions, and a steep slope at its lower side wall portions. The mouth of the groove underlies a hole formed in an SiO 2 film on an Si epitaxial layer, which hole underlies, and is larger than, a hole formed in an Si 3 N 4 film on the SiO 2 film. This groove provides gentle steps at its mouth but occupies small area on the substrate, thus enabling an extremely high-density integrated circuit to be formed. Recently, with the advance of the microminiaturization of the semiconductor integrated circuit devices, the distance between element separating regions has become narrower and narrower for each generation. To cope with the narrower element separating regions, the buried element separation has been developed. Figs. 3(A) to 3(D) are cross-sectional views for assistance in explaining the conventional method of manufacturing the buried element separating region, in particular. First, as shown in Fig. 3(A), a SiO 2 film 2 with a thickness of about 10 nm, for instance is formed on a Si substrated by thermal oxidization. Then, a resist film 5 is applied onto the SiO 2 film 2, and further the resist film 5 is formed into a predetermined shape in accordance with photolithography. Further, by using the formed resist film 5 as a mask, an element separating trench 7 with a depth of about 500 nm, for instance is formed in the SiO 2 film 2 and the Si substrate by anisotropic etching. Successively, as shown in Fig. 3(B), to eliminate damage caused by etching, another SiO 2 film 8 with a thickness of a bout 20 nm, for instance is deposited thereon by thermal oxidization. After that, another SiO 2 9 film with a thickness of about 1 µm, for instance is further deposited thereon as a trench filling substance. Further, as shown in Fig. 3(C), the deposited filling substance of the SiO 2 film 9 is etched back by anisotropic etching or polishing to complete the buried element separating region 10. Further, as shown in Fig. 3(D), after the ion implantation process to control the threshold value of a MOSFET, a gate oxide film 11 with a thickness of about 10 nm is formed thereon by thermal oxidization. Further, a poly crystalline Si film 12 with a thickness of about 300 nm, for instance is formed into a predetermined shape as a gate electrode. In the above-mentioned conventional method of manufacturing the buried element separating region 10, since a process margin must be taken into account in the etching back process shown in Fig. 3(C), a predetermined overetching is inevitably required in Fig. 3(C), with the result that the surface of the buried element separating region 10 is formed being slightly recessed from the surface of the Si substrate 1. Therefore, as shown in Fig. 3(D), an edge portion 13 remains at the buried element separating region 10, so that the gate oxide film 11 formed thereon is also formed with an edge portion 13. As described above, in the conventional method of manufacturing the semiconductor device, since a stepped portion is generated at the edge portion 13 of the buried element separating region 10 and thereby also at the edge portion of the gate oxide film 11 in the same way, an electric field is inevitably concentrated at this edge portion 13 of the buried element separating region 10. Once the electric field concentration occurs as described above, the characteristics between gate voltage and drain current deteriorate, as shown by a solid line curve in Fig. 4, which is referred to as kink characteristics in comparison with the normal characteristics as shown by dashed lines. The kink characteristics occur because the characteristics of a parasitic transistor are added to the original I-V characteristics of the MOSFET. On the other hand, since the edge portion 13 is a corner of the Si substrate as shown in Fig. 3(D), a mechanical stress tends to be concentrated and thereby a defect tends to occur easily at the edge portion 13, thus causing a problem in that a leakage tends to occur in the gate oxide film 11. Accordingly, it is the object of the present invention to provide a method of manufacturing semiconductor devices, which can realize buried element separations suitable for microminiaturized integrated circuits, without forming defects which may cause electric field concentration and gate oxide film leakage. According to the invention there is provided a method of manufacturing a semiconductor device, comprising the steps of: forming a first material layer and a second material layer in sequence on a surface of a semiconductor substrate; forming a first opening in the second material layer and a second opening in the first material layer, the second opening underlying, and being larger than, the first opening; forming an element separating trench under the second opening in the substrate by using the second material layer as a mask; removing the second material layer; depositing a filling material on the first material layer so as to fill said trench; and etching back the filling material by using the first material layer as a stopper. In the manufacturing method to be described in more detail below, since the first opening of the first layer deposited on the semiconductor substrate is determined to be broader than the opening of the element separating trench formed on the semiconductor substrate, it is possible to cover the edge portion (formed between the substrate surface and the element separating trench) with a filling substance deposited in the trench and on the surface of the semiconductor substrate. As a result, it is possible to eliminate defects which may cause the electric field concentration and the gate oxide film leakage at the edge portion. For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figs. 1(A) to 1(G) are cross-sectional views for assistance in explaining a first preferred method of performing the invention, for manufacturing semiconductor devices; Figs. 2(A) to 2(G) are cross-sectional views for assistance in explaining a second preferred method of performing the invention, for manufacturing semiconductor devices; Figs. 3(A) to 3(D) are cross-sectional views for assistance in explaining a conventional method of manufacturing semiconductor devices; and Fig. 4 shows I-V characteristics of the semiconductor device formed in the conventional manufacturing method. Preferred ways of putting the present invention into effect will be described hereinbelow with reference to the attached drawings. Fig. 1(A) to (G) show a first way of putting into effect the manufacturing method according to the present invention. First, as shown in Fig. 1(A), a SiO 2 film 2 with a thickness of about 10 nm, for instance is formed on a Si substrate 1 by thermal oxidization. Then, a poly crystalline Si film 3 with a thickness of about 200 nm, for instance is deposited by chemical vapor deposition method. Further, a SiO 2 film 4 with a thickness of about 200 nm, for instance is deposited thereon by chemical vapor deposition method. After that, a resist film 5 is applied onto the SiO 2 film 4, and then the resist film 5 is formed into a predetermined shape in accordance with photolithography. Further, as shown in Fig. 1(B), by using the formed resist film 5 as a mask, the SiO 2 film 4 and the poly crystalline Si film 3 are both processed by anisotropic etching in sequence to remove the resist film 5. After that, the poly crystalline Si film 3 is etched back by isotropic etching to form a recessed portion 6 with a recession of about 100 nm, for instance. As a method of forming the recessed portion 6, CDE method (chemical dry etching), wet processing, etc. are known. In any method, however, it is possible to form the recessed portion 6 as shown in Fig. 1(B). After that, as shown in Fig. 1(C), the SiO 2 film 2 is removed, and further the Si substrate 1 is etched to form an element separating trench 7 with a depth of about 500 nm (so that a buried element separating region can be formed later). Further, in this process, when the SiO 2 film 2 is removed, although the SiO 2 film 4 (used as a mask for etching the Si substrate 1) is also etched simultaneously, since the film thickness (10 nm) of the SiO 2 film 2 is sufficiently thinner than that (200 nm) of the SiO 2 film 4 (used as an etching mask), the thickness of the SiO 2 film 4 can be almost maintained. Next, as shown in Fig. 1(D), after the SiO 2 film 4 has been removed by use of NH 4 F solution, a SiO 2 film 8 with a thickness of about 20 nm is formed by thermal oxidization in order to remove defects produced on the Si substrate 1 when the Si substrate 1 is etched. After that, another SiO 2 film 9 with a thickness of about 1 µm, for instance is further deposited thereon by chemical vapor deposition method as a filling substance of the element separating trench 7 (as a buried element separation). After that, as shown in Fig. 1(E), the deposited filling substance of SiO 2 film 9 is etched back by anisotropic etching or polishing by use of the poly crystalline Si film 3 as a stopper film, the etching of the filling substance SiO 2 film 9 can be stopped at a level flush with the poly crystalline Si film 3 to form the buried element separating region 10. Further, as shown in Fig. 1(F), the poly crystalline Si film 3 used as a stopper during the etching back is removed to complete the buried element separating region 10. Finally, as shown in Fig. 1(G), a poly crystalline Si film 12 is deposited all over the device to complete a semiconductor device. The buried element separating region 10 formed in accordance with the above-mentioned method is of concave shape. In addition, since the edge portion 13 of the Si substrate 1 is covered with the SiO 2 film 9 for filling the buried element separating trench 7, it is possible to eliminate electric field concentration and defects at the corner thereof, so that it is possible to realize an LSI of high reliability. Further, in the above-mentioned method, the SiO 2 film 4 is used as a mask for etching the Si substrate 1 to form the element separating trench 7, and the poly crystalline Si film 3 is used as an etching stopper film when the filling substance of the buried element separating region 10 is etched back. Without being limited thereto, however, it is possible to use any other films, as far as the etching mask (used when the Si substrate 1 is etched to form the element separating trench 7) and the etching stopper (used when the filling substance is etched back) are different from each other. For instance, a WSi film, TiN film, carbon film, SiN film, etc. are usable as the etching stopper. Further, in this first method, the SiO 2 is used as the substance for filling the buried element separating trench 7. Without being limited only thereto, it is of course possible to use other filling substances such as Si, SiN, etc. Further, when Si is used as the filling substance, SiO 2 film and SiN film can be used as the poly crystalline Si film 3 and the SiO 2 film 4, both shown in Fig. 1(A), or vice versa. Further, in the first method, the poly crystalline Si film 3 and the SiO 2 film 4 are deposited in sequence; these films 3 and 4 are etched by use of a resist film 5 formed into a predetermined shape as a mask; and the SiO 2 film 4 is used as a mask to etch the element separating trench 7. However, it is possible to realize the same structure even when the SiO 2 film 4 is not deposited. Fig. 2(A) to (C) show a second preferred way of putting into effect the manufacturing method according to the present invention, which is described from the above-mentioned point of view. First, as shown in Fig. 2(A), a SiO 2 film 2 with a thickness of about 10 nm, for instance is formed on a Si substrate 1 by thermal oxidization. Then, a poly crystalline Si film 3 with a thickness of about 200 nm, for instance is deposited by chemical vapor deposition method. Further, a resist film 5 is applied thereonto and formed into a predetermined shape in accordance with photolithography. Further, as shown in Fig. 2(B), by using the formed resist film 5 as a mask, the poly crystalline Si film 3 is processed by anisotropic etching, and further etched by isotropic etching to form a recessed portion 6 with a recess of about 100 nm. As a method of forming the recessed portion 6, CDE method (chemical dry etching), wet processing, etc. are known. In any method, however, it is possible to form the recessed portion 6 as shown in Fig. 2(B). After that, as shown in Fig. 2(C), the SiO 2 film 2 is removed to expose the surface of the Si substrate 1, and the exposed Si substrate 1 is etched to a depth of about 500 nm (sufficient depth as the buried element separation) by use of the SiO 2 film 2 as a mask to form an element separating trench 7. After that, as shown in Fig. 3A the SiO 2 film 2 is removed and the process as shown in Fig. 1(D) to (G) are conducted in the same way as with the case of the first embodiment to obtain the semiconductor device. As described above, in the above-mentioned methods, as shown in Fig. 1 (F), after the buried element separating region 10 has been completed, ions are implanted to control the threshold level to a predetermined value; after the SiO 2 film 2 and the SiO 2 film 8 above the surface of the Si substrate 1 has been removed, a gate oxide film 11 with a thickness of about 10 nm is formed by thermal oxidization; and after that, a poly crystalline Si film 12 with a thickness of about 300 nm, for instance is deposited and formed into a predetermined shape as a gate electrode. The device thus obtained is shown in Fig. 1(G). When the structure shown in Fig. 1(G) is compared with that shown in Fig. 3(D), since the edge portion 13 is formed into a concave shape as shown in Fig. 1(G), it is possible to solve the problem with the kink characteristics of the MOSFET caused by the electric field concentration at the edge portion 13 of the buried element separating region 10 in the conventional semiconductor device. Further, in the conventional semiconductor device shown in Fig. 3(D), since the edge portion 13 is located at the corner of the Si substrate 1, a mechanical stress tends to be concentrated and thereby a defect easily occurs, so that a problem arises in that the gate oxide film is leaked. In contrast with this, in the semiconductor device of the present invention as shown in Fig. 1(G), since the edge portion 13 of the buried element separating region 10 is formed away from the corner of the Si substrate 1, it is possible to prevent a defect from being produced at the edge portion 13 and thereby to solve the problem related to the gate oxide film leakage. Further, it is also possible to use a Si nitride film instead of the SiO 2 films 2, 4 and 8. Further, it is also possible to use both the SiO 2 film and Si nitride film in combination. Further, the SiO 2 film 2 can be replaced with a carbon film, TiN film, or siliside metal, etc. Further, the SiO 2 film 4 can be replaced with Si oxide film, Si nitride film, Si film, or resist film, etc. Further, the SiO 2 film 8 can be replaced with Si oxide film, Si nitride film, or Si film. As described above, in the methods described of manufacturing the semiconductor device, after materials are deposited in sequence on the substrate, a part of the material is recessed in the horizontal direction along the surface of the substrate to form a recessed portion; after that, an element separating trench is formed; another material is deposited; and the whole device is etched back. Therefore, since a convex buried element separating region 10 can be formed and in addition since the edge portion of the substrate can be covered with the element separating region filling material, it is possible to prevent the electric field from being concentrated at the corner portion of the substrate and to prevent a defect from occurring at the corner portion of the substrate, thus providing miniaturized semiconductor device of higher reliability. In summary, since the edge portion of the element separating trench formed in the semiconductor substrate can be covered with the trench filling material, it is possible to provide a semiconductor device which can suppress electric field concentration at the edge portion of the substrate and thereby to prevent the defect from being produced at the edge portion thereof.

Claims: A method of manufacturing a semiconductor device, comprising the steps of: forming a first material layer (3) and a second material layer (4; 5) in sequence on a surface of a semiconductor substrate (1); forming a first opening in the second material layer (4; 5) and a second opening in the first material layer (3), the second opening underlying, and being larger than, the first opening; forming an element separating trench (7) under the second opening in the substrate (1) by using the second material layer (4; 5) as a mask; removing the second material layer (4; 5); depositing a filling material (9) on the first material layer (3) so as to fill said trench (7); and etching back the filling material (9) by using the first material layer (3) as a stopper. The method of manufacturing a semiconductor device according to claim 1, which further comprises the steps of: removing the first material layer (3); and depositing a third material layer (12) on the filling material (9) in the trench (7) and the substrate (1). The method of manufacturing a semiconductor device according to claim 2, wherein the first material layer (3) is any one of a poly crystalline silicon layer, a SiO 2 layer, and a SiN layer; the second material layer (5) is a resist film; the third material layer (12) is a poly crystalline silicon film; and the filling material (9) is any of a SiO 2 film and a Si film. The method of manufacturing a semiconductor device according to claim 3, wherein the first material layer (3) is a SiO 2 layer and the filling material (9) is a SiO 2 film, and the method further comprises the step of forming a first insulating layer (2) on the substrate (1) before the first material layer (3) is formed. The method of manufacturing a semiconductor device according to claim 3, wherein the first material layer (3) is SiN layer and the filling material (9) is a SiO 2 film. A method of manufacturing a semiconductor device according to claim 1, further comprising the steps of: forming a third material layer 5 on the second material layer (3) before the first opening is formed; patterning the third material layer (5); and etching the second and the first material layers (4, 3) by using the third material layer (5) as a mask to form the first opening in the second material layer (4) and the second opening in the first material layer (3). The method of manufacturing a semiconductor device according to claim 6 which further comprises the steps of: removing the first material layer (3); and depositing a fourth material layer (12) on the filling material (9) in the trench (7) and the substrate (1). The method of manufacturing a semiconductor device according to claim 1 or 6, which further comprises the steps of forming a first insulating layer (2) on the substrate (1) before the first material layer (3) is formed. The method of manufacturing a semiconductor device according to claim 1, 6 or 8, wherein a second insulating layer (8) is formed on the first insulating layer (3) and on the inside surfaces of the trench before the filling material (9) is deposited. The method of manufacturing a semiconductor device of claim 2 or 7, wherein a third insulating layer (11) is formed on the substrate (1) and the filling material (9) filling the trench (7) before the fourth material layer (12) is deposited. The method of manufacturing a semiconductor device according to claim 7, wherein the first material layer (3) is any one of a poly crystalline silicon layer, a SiO 2 layer, and a SiN layer; the second material layer (4) is any of a SiO 2 film and a SiN film; the third material layer (5) is a resist film; and the filling material (9) is any of a SiO film and a Si film. The method of manufacturing a semiconductor device according to claim 11, wherein the first material layer (3) is a polycrystalline silicon layer, the second material layer (4) is a SiO 2 film and the filling material (9) is a SiO 2 film, and the method further comprises the step of forming a first insulating layer (2) of a SiO 2 film on the substrate (1) before the first material layer (3) is formed. The method of manufacturing a semiconductor device according to claim 11, wherein the first material layer (3) is a polycrystalline silicon layer, the second material layer (4) is a SiN film and the filling material (9) is a SiO 2 film, and the method further comprises the step of forming a first insulating layer (2) of a SiO 2 film on the substrate (1) before the first material layer (3) is formed.

Inventors: MATSUOKA FUMITOMO, MATSUOKA, FUMITOMO
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1994
Main classification: H01L21
IPC codes: H01L21